Abstract:

An internal combustion engine including a cylinder with bore and a piston
disposed to reciprocate in the bore is operated by moving the piston in
the bore between top and bottom dead center positions and applying
lubricant to a portion of the piston that protrudes from the bore.
Lubricant is wiped from the piston as the piston travels into the bore
toward its top dead center position.

Claims:

1. A method of operating an engine including a piston with a skirt that
reciprocates in a bore, the method comprising:moving the piston in the
bore between top and bottom dead center positions, such that at least a
portion of the piston skirt protrudes out of the bore as the piston moves
toward its bottom dead center position; andapplying lubricant to an
external surface portion of the piston skirt that protrudes from the bore
as the piston skirt protrudes from the bore.

2. A method of operating an engine including a cylinder with bore and a
piston with a piston disposed to reciprocate in the bore, the method
comprising:moving the piston in the bore between top and bottom dead
center positions;applying lubricant to a portion of the piston skirt;
and,wiping lubricant from the portion as the piston travels toward its
top dead center position.

3. The method of claim 2, wherein applying lubricant includes applying
lubricant to an external surface portion of the piston skirt and wiping
lubricant includes wiping lubricant from the external surface portion.

4. The method of claim 3, wherein wiping lubricant from the external
surface portion includes wiping lubricant from the external surface
portion with a ring.

5. The method of claim 4, wherein wiping lubricant from the external
surface portion with a ring includes wiping lubricant from the piston
with a ring located in an annular groove in the bore.

6. A method of operating a diesel engine including a cylinder with bore,
exhaust and inlet ports, and ends, and first and second opposed pistons
disposed to reciprocate in the bore, the method comprising:moving the
pistons in the bore between top and bottom dead center positions;applying
lubricant to the pistons as they move between the top and bottom dead
center positions;wiping lubricant from the first piston with a first ring
located in the bore between a first end of the cylinder and the exhaust
port as the first piston travels into the bore; and,wiping lubricant from
the second piston with a second ring located in the bore between a second
end of the cylinder and the inlet port as the second piston travels into
the bore.

7. The method of claim 6, further including injecting fuel into the
cylinder through a site on the cylinder between the exhaust and inlet
ports when the pistons are near the top dead center positions.

8. An assembly for a diesel engine, comprising:a cylinder with a bore,
exhaust and inlet ports, and first and second ends;first and second
opposed pistons disposed to reciprocate in the bore;each piston including
a skirt and a crown; and,a first ring located outboard of the exhaust
port to contact and wipe the skirt of the first piston, and a second ring
located outboard of the inlet port to contact and wipe the skirt of the
second piston.

9. The assembly of claim 8, further including a first annular groove in
the bore between the first end of the cylinder and the exhaust port and a
second annular groove in the bore between a second end of the cylinder
and the inlet port, wherein the first ring is in the first annular groove
and the second ring is in the second annular groove.

10. The assembly of claim 9, wherein each of the first and second rings is
a polymeric ring.

11. The assembly of claim 9, further including an injection site on the
cylinder, between the exhaust and inlet ports and a fuel injector coupled
to the injection site.

12. The assembly of claim 9, the cylinder further including an exhaust
manifold at the first end, an intake manifold at the second end, and
lubricant dispensers outboard of the exhaust and intake manifolds.

13. The assembly of claim 9, the cylinder including a cylinder tube with
first and second axial ends and exhaust and inlet manifolds joined to
respective ends of the cylinder tube, the exhaust manifold including an
annular gallery that constitutes the exhaust port, and the intake
manifold including an annular gallery that constitutes the inlet port.

14. The assembly of claim 13, wherein each of the annular galleries has
the shape of a scroll.

15. The assembly of claim 9, further including a bridge on an end of each
piston for linking the piston to connecting rods.

16. The assembly of claim 15, further including an injection site on the
cylinder, between the exhaust and inlet ports and a fuel injector coupled
to the injection site.

17. An internal combustion engine, comprising:a cylinder including a bore,
exhaust and inlet ports, and first and second ends;first and second
opposed pistons disposed to reciprocate in the bore;a pair of
crankshafts;rods connecting the pistons to the crankshafts; and,a first
ring located in the bore between the first end of the cylinder and the
exhaust port to contact and wipe lubricant from the first piston, and a
second ring located in the bore between the second end of the cylinder
and the inlet port to contact and wipe lubricant from the second piston.

18. The engine of claim 17, further including a first annular groove in
the bore between the first end of the cylinder and the exhaust port and a
second annular groove in the bore between a second end of the cylinder
and the inlet port, wherein the first ring is in the first annular groove
and the second ring is in the second annular groove.

19. The engine of claim 18, wherein the first and second rings are
polymeric rings.

20. The engine of claim 18, further including an injection site on the
cylinder, between the exhaust and inlet ports and a fuel injector coupled
to the injection site.

21. The engine of claim 17, further including an injection site on the
cylinder, between the inlet and exhaust ports and a fuel injector coupled
to the injection site.

22. The engine of claim 17, the cylinder including an exhaust manifold at
the first end, an intake manifold at the second end, and lubricant
dispensers located outboard of the exhaust and intake manifolds.

23. The engine of claim 17, the cylinder including a cylinder tube with
first and second axial ends and exhaust and inlet manifolds joined to the
first and second axial ends respectively, the exhaust manifold including
an annular gallery that constitutes the exhaust port, and the intake
manifold including an annular gallery that constitutes the inlet port.

24. The engine of claim 23, further including dispensers located outboard
of the exhaust and inlet manifolds to apply liquid coolant to the crowns
and internal skirts of the first and second pistons.

25. The engine of claim 24, further including an injection site on the
cylinder, between the exhaust and inlet ports and a fuel injector coupled
to the injection site.

Description:

PRIORITY

[0001]This is a continuation of U.S. patent application Ser. No.
11/642,140, filed Dec. 20, 2006, which is a continuation of U.S. patent
application Ser. No. 10/865,707, filed Jun. 10, 2004, now U.S. Pat. No.
7,156,056.

RELATED APPLICATIONS

[0002]The following co-pending applications, all commonly assigned to the
assignee of this application, contain subject matter related to the
subject matter of this application.

[0013]The invention concerns a method and an apparatus for an internal
combustion engine. More particularly, the invention relates to a
two-stroke, opposed-piston engine.

[0014]The opposed piston engine was invented by Hugo Junkers around the
end of the nineteenth century. Junkers' basic configuration, shown in
FIG. 1, uses two pistons P1 and P2 disposed crown-to-crown in a common
cylinder C having inlet and exhaust ports I and E near bottom dead center
of each piston, with the pistons serving as the valves for the ports.
Bridges B support transit of the piston rings past the ports I and E. The
engine has two crankshafts C1 and C2, one disposed at each end of the
cylinder. The crankshafts, which rotate in the same direction, are linked
by rods R1 and R2 to respective pistons. Wristpins W1 and W2 link the
rods to the pistons. The crankshafts are geared together to control
phasing of the ports and to provide engine output. Typically, a
turbo-supercharger is driven from the exhaust port, and its associated
compressor is used to scavenge the cylinders and leave a fresh charge of
air each revolution of the engine. The advantages of Junkers' opposed
piston engine over traditional two-cycle and four-cycle engines include
superior scavenging, reduced parts count and increased reliability, high
thermal efficiency, and high power density. In 1936, the Junkers Jumo
airplane engines, the most successful diesel engines to date, were able
to achieve a power density and fuel efficiency that have not been matched
by any diesel engine since. According to C. F. Taylor (The
Internal-Combustion Engine in Theory and Practice: Volume II, revised
edition; MIT Press, Cambridge, Mass., 1985): "The now obsolete Junkers
aircraft Diesel engine still holds the record for specific output of
Diesel engines in actual service (Volume I, FIG. 13-11)."

[0015]Nevertheless, Junkers' basic design contains a number of
deficiencies. The engine is tall, with its height spanning the lengths of
four pistons and at least the diameters of two crankshafts, one at each
end of the cylinders. A long gear train with typically five gears is
required to couple the outputs of the two crankshafts to an output drive.
Each piston is connected to a crankshaft by a rod that extends from the
interior of the piston. As a consequence the rods are massive to
accommodate the high compressive forces between the pistons and
crankshafts. These compressive forces, coupled with oscillatory motion of
the wrist pins and piston heating, cause early failure of the wrist pins
connecting the rods to the pistons. The compressive force exerted on each
piston by its connecting rod at an angle to the axis of the piston
produces a radially-directed force (a side force) between the piston and
cylinder bore. This side force increases piston/cylinder friction,
raising the piston temperature and thereby limiting the brake mean
effective pressure (BMEP) achievable by the engine. One crankshaft is
connected only to exhaust side pistons, and the other only to inlet side
pistons. In the Jumo engine the exhaust side pistons account for up to
70% of the torque, and the exhaust side crankshaft bears the heavier
torque burden. The combination of the torque imbalance, the wide
separation of the crankshafts, and the length of the gear train coupling
the crankshafts produces torsional resonance effects (vibration) in the
gear train. A massive engine block is required to constrain the highly
repulsive forces exerted by the pistons on the crankshafts during
combustion, which literally try to blow the engine apart.

[0016]One proposed improvement to the basic opposed-piston engine,
described in Bird's U.K. Patent 558,115, is to locate the crankshafts
beside the cylinders such that their axes of rotation lie in a plane that
intersects the cylinders and is normal to the axes of the cylinder bores.
Such side-mounted crankshafts are closer together than in the Jumo
engines, and are coupled by a shorter gear train. The pistons and
crankshafts are connected by rods that extend from each piston along the
sides of the cylinders, at acute angles to the sides of the cylinders, to
each of the crankshafts. In this arrangement, the rods are mainly under
tensile force, which removes the repulsive forces on the crankshafts and
yields a substantial weight reduction because a less massive rod
structure is required for a rod loaded with a tensile force than for a
rod under a mainly compressive load of the same magnitude. The wrist pins
connecting the rods to the pistons are disposed outside of the pistons on
saddles mounted to the outer skirts of the pistons. Bird's proposed
engine has torsional balance brought by connecting each piston to both
crankshafts. This balance, the proximity of the crankshafts, and the
reduced length of the gear train produce good torsional stability. To
balance dynamic engine forces, each piston is connected by one set of
rods to one crankshaft and by another set of rods to the other
crankshaft. This load balancing essentially eliminates the side forces
that otherwise would operate between the pistons and the internal bores
of the cylinders. The profile of the engine is also reduced by
repositioning the crankshafts to the sides of the cylinders, and the
shorter gear train requires fewer gears (four) than the Jumo engine.
However, even with these improvements, a number of problems prevent
Bird's proposed engine from reaching its full potential for
simplification and power-to-weight ratio ("PWR", which is measured in
horsepower per pound, HP/lbs).

[0017]The favorable PWR of opposed piston engines as compared with other
two and four cycle engines results mainly from the simple designs of
these engines which eliminate cylinder heads, valve trains, and other
parts. However, reducing weight alone has only a limited ability to boost
PWR because at any given weight, any increase in BMEP to increase power
is confined by the limited capability of the engines to cool the pistons.

[0018]Combustion chamber heat is absorbed by pistons and cylinders. In
fact the crown of a piston is one of the hottest spots in a two-cycle,
opposed-piston compression-ignition engine. Excessive piston heat will
cause piston seizure. The piston must be cooled to mitigate this threat.
In all high performance engines, the pistons are cooled principally by
rings mounted to the outside surfaces of the pistons, near their crowns.
The rings of a piston contact the cylinder bore and conduct heat from the
piston to the cylinder, and therethrough to a coolant flowing through a
cooling jacket or by cooling fins on the engine cylinder assembly.
Intimate contact is required between the rings and cylinder bore to cool
the piston effectively. But piston rings must be lightly loaded in
two-cycle, ported engines in order to survive transit over the bridges of
the cylinder ports, where very complex stresses occur. Therefore, the
rings are limited in their ability to cool the pistons, which places a
limit on the maximum combustion chamber temperature achievable before
engine failure occurs. It is clear that, without more effective piston
cooling, BMEP cannot be increased in an opposed piston engine without
endangering the engine's operation.

[0019]Prior engines include an engine block in which cylinders and engine
bearings are cast in a large passive unit that serves as the primary
structural and architectural element of the engine. Although Bird's
engine rectified torque imbalance, eliminated compressive forces on the
rods, and eliminated side forces on the cylinder bore, it still used the
engine block as the primary structural element, providing support for the
cylinders, manifolds for cylinder ports, and cooling jackets for the
cylinders and for retaining the engine bearings. But thermal and
mechanical stresses transmitted through the engine block cause
non-uniform distortion of the cylinders and pistons necessitating piston
rings to assist in maintaining the piston/cylinder seal.

SUMMARY

[0020]A method for operating and internal combustion engine having a
cylinder with bore and a piston disposed to reciprocate in the bore
includes moving the piston in the bore between top and bottom dead center
positions, applying lubricant to a portion of the piston, and wiping
lubricant from the piston with a ring as the piston travels toward its
top dead center position.

[0021]A cylinder for an internal combustion engine includes a bore and
exhaust and opposing ends. A pair of opposed pistons is disposed to
reciprocate in the bore. Rings located are located to contact and wipe
lubricant from the pistons as they travel into the bore toward top dead
center positions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]The below-described drawings are meant to illustrate principles and
examples discussed in the following detailed description. They are not
necessarily to scale.

[0023]FIG. 1 is a partially schematic illustration of a portion of a prior
art opposed piston diesel engine.

[0024]FIGS. 2A and 2B are side sectional views of a cylinder with opposed
pistons coupled by tensile-loaded connecting rods to two crankshafts.
FIG. 2A shows the pistons at inner, or top dead center. FIG. 2B shows the
pistons at outer, or bottom dead center.

[0025]FIGS. 3A-3F are schematic sectional illustrations of the cylinder
and pistons of FIGS. 2A and 2B illustrating a complete cycle of the
pistons.

[0026]FIG. 4 is a plot showing relative phasing of the two opposed pistons
of FIGS. 3A-3F.

[0027]FIG. 5A is a side sectional view of the cylinder with opposed
pistons of FIGS. 2A and 2B rotated 90° on its axis. FIG. 5B is the
same view of the cylinder in FIG. 5A showing an alternate embodiment for
cooling the cylinder.

[0028]FIGS. 6A and 6B are side perspective views showing increasingly
complete stages of assembly of a single cylinder mechanism for an
opposed-piston engine.

[0029]FIGS. 7A-7C are perspective views of a single-cylinder
opposed-piston engine module showing assembly details at increasingly
complete stages of assembly. FIG. 7D is an end view of the
single-cylinder opposed-piston engine module showing an open gearbox with
one gear partially cut away.

[0031]FIG. 9A is a schematic diagram of a supply system for an
opposed-piston engine which provides liquid coolant to the engine. FIG.
9B is a schematic diagram of a combined fuel and coolant supply system
for an opposed-piston engine. FIG. 9C is a schematic diagram of another
supply system for an opposed-piston engine which provides liquid coolant
to the engine.

[0032]FIG. 10 is a schematic diagram of gas flow in an opposed-piston
engine.

[0034]Components of our new opposed piston engine are illustrated in FIGS.
2A and 2B. These figures show a cylinder 10 with opposed pistons 12 and
14 disposed therein. The pistons 12 and 14 move coaxially in the cylinder
10 in opposed motions, toward and away from each other. FIG. 2A
illustrates the pistons 12 and 14 at top (or inner) dead center where
they are at the peak of their compression strokes, near the moment of
ignition. FIG. 2B illustrates the pistons near bottom (or outer) dead
center, where they are at the end of their expansion or power strokes.
These and intermediate positions will be described in more detail below.

[0035]The following explanation presumes a compression-ignition engine for
the sake of illustration and example only. Those skilled in the art will
realize that the elements, modules and assemblies described may also be
adapted for a spark-ignition engine.

[0036]As shown in FIGS. 2A and 2B, the cylinder 10 is a tube with the
opposed pistons 12 and 14 disposed in it for reciprocating opposed motion
toward and away from each other and the center of the cylinder 10. The
pistons 12 and 14 are coupled to first and second side-mounted
counter-rotating crankshafts 30 and 32 which, in turn, are coupled to a
common output (not shown in these figures).

[0037]The pistons 12 and 14 are hollow cylindrical members with closed
axial ends 12a and 14a which terminate in crowns 12d and 14d, open axial
ends 120 and 140, and skirts 12s and 14s which extend from the open axial
ends 120 and 140 to the crowns 12d and 14d. Saddles 16 and 18, in the
form of open annular structures, are mounted to the open axial ends 120
and 140 of the pistons 12 and 14, respectively. Each of the saddles 16,
18 connects ends of a plurality of connecting rods to the respective
piston on which it is mounted. The perspective of these figures
illustrates only two connecting rods for each piston, and it is to be
understood that one or more additional connecting rods are not visible.
The connecting rods 20a and 20b are connected to the saddle 16 near the
open end of the piston 12, while the connecting rods 22a and 22b are
connected to the saddle 18 near the open end of the piston 14. Because
the saddles 16 and 18 provide linkage between the pistons 12 and 14 and
their respective rods, the pistons lack internal wristpins. The resulting
open structure of the saddles and the pistons permits coolant dispensers
24 and 26 to extend axially into the pistons 12 and 14 from the open ends
12o and 14o to be aimed at the crowns and internal skirts of the pistons
12 and 14, respectively.

[0038]The two side-mounted crankshafts 30 and 32 are disposed with their
axes parallel to each other and lying in a common plane that intersects
the cylinder 10 at or near its longitudinal center and that is
perpendicular to the axis of the cylinder. The crankshafts rotate in
opposite directions. The connecting rods 20a, 20b and 22a, 22b are
connected to crank throws on the crankshafts 30 and 32. Each connecting
rod is disposed to form an acute angle with respect to the axes (and the
sides) of the cylinder 10 and the pistons 12 and 14. The connecting rods
are linked to the saddles 16 and 18 by means of needle bearings 36, and
to the crank throws by means of roller bearings 38. As each piston moves
through the operational cycle of the engine, the ends of the connecting
rods coupled to the piston's saddle oscillate through an angular path,
and there is no complete revolution between those ends and the elements
of the saddle to which they are coupled. Needle bearings with
sufficiently small diameter rollers produce at least full rotation of the
rollers during each oscillation, thereby reducing wear asymmetry and
extending bearing life.

[0039]The geometric relationship between the connecting rods, saddles, and
crankshafts in FIGS. 2A and 2B keeps the connecting rods principally
under tensile stress as the pistons 12 and 14 move in the cylinder 10,
with a limited level of compressive stress resulting from inertial forces
of the pistons at high engine speeds. This geometry substantially, if not
entirely, eliminates side forces between the pistons and the bore of the
cylinder.

[0040]In FIGS. 2A and 2B, additional details and features of the cylinder
10 and the pistons 12 and 14 are shown. The cylinder 10 includes an inlet
port 46 through which air, under pressure, flows into the cylinder 10.
The cylinder also has an exhaust port 48 through which the products of
combustion flow out of the cylinder 10. Because of their locations with
respect to these ports, the pistons 12 and 14 may be respectively
referred to as the "exhaust" and "inlet" pistons, and the ends of the
cylinder 10 may be similarly named. A preferred, but by no means the only
possible, configuration for the ports 46 and 48 are described below. The
operations of the exhaust and inlet ports are modulated by movement of
the pistons during engine operation. At least one injection site (not
shown in this drawing) controlled by one or more fuel injectors
(described below) admits fuel into the cylinder 10.

[0041]As the following illustrations and description will establish, the
relation between piston length, the length of the cylinder, and the
length added to the cylinder bore by the cylinder manifolds, coupled with
a phase difference between the pistons as they traverse their bottom dead
center positions, modulate port operations and sequence them correctly
with piston events. In this regard, the inlet and exhaust ports 46 and 48
are displaced axially from the longitudinal center of the cylinder, near
its ends. The pistons may be of equal length. Each piston 12 and 14 keeps
the associated port 46 or 48 of the cylinder 10 closed until it
approaches its bottom dead center position. The phase offset between the
bottom dead center positions produces a sequence in which the exhaust
port opens when the exhaust piston moves near its bottom dead center
position, then the inlet port opens when the inlet piston moves near its
bottom dead center position, following which the exhaust port closes
after the exhaust piston moves away from its bottom dead center position,
and then the inlet port closes after the inlet piston moves away from its
bottom dead center position.

[0042]FIGS. 3A-3F are schematic representations of the cylinder 10 and
pistons 12 and 14 of FIGS. 2A and 2B illustrating a representative cycle
of operation ("operational cycle"). In this example, with the pistons at
top dead center, the opposing rods on each side of the cylinder form an
angle of approximately 120° as shown in FIG. 3A. This geometry is
merely for the purpose of explaining an operational cycle; it is not
meant to exclude other possible geometries with other operating cycles.
For convenience, an operational cycle may be measured rotationally,
starting at a crank angle of 0° where the pistons are at top dead
center as shown in FIG. 3A and ending at 360°. With reference to
FIG. 3A, the term "top dead center" is used to refer to the point at
which the closed ends 12a and 14a of the pistons 12 and 14 are closest to
each other and to the crankshafts and air is most highly compressed in
the cylinder space 42 between the ends. This is the top of the
compression stroke of both pistons. Using a convenient measurement, top
dead center occurs at 0° of the cycle of operation. Further, with
reference to FIGS. 3C and 3E, the term "bottom dead center" refers to the
points at which the closed ends 12a and 14a of the pistons 12 and 14 are
farthest from the crankshafts 30 and 32. Bottom dead center for the
piston 12 occurs just before 180° of the cycle of operation.
Bottom dead center for the piston 14 occurs just after 180° of the
cycle of operation.

[0043]A two-stroke, compression-ignition operational cycle is now
explained with reference to FIGS. 3A-3F. This explanation is meant to be
illustrative, and uses 360° to measure a full cycle. The events
and actions of the cycle are referenced to specific points in the
360° cycle with the understanding that for different geometries,
while the sequence of events and actions will be the same, the points at
which they occur in the 360° cycle will differ from those in this
explanation.

[0044]Referring now to FIG. 3A, prior to the 0° reference point in
the operational cycle where the pistons 12 and 14 will be at top dead
center, fuel is initially injected into the cylinder through the at least
one injection site. Fuel may continue to be injected after combustion
commences. The fuel mixes with compressed air and the mixture ignites
between the closed ends 12a and 14a, driving the pistons apart in a power
stroke, to drive the crankshafts 30 and 32 to rotate in opposite
directions. The pistons 12 and 14 close the inlet and exhaust ports 46
and 48 during the power stroke, blocking air from entering the inlet port
and exhaust from leaving the exhaust port. In FIG. 3B, at 90° in
the operational cycle, the pistons 12 and 14, near midway through their
power strokes, continue to travel out of the cylinder 10. The inlet and
exhaust ports 46 and 48 are still closed. In FIG. 3c, at 167° in
the operational cycle, the closed end 12a of the piston 12 has moved far
enough out of the cylinder 10 to open the exhaust port 48, while the
inlet port 46 is still closed. The products of combustion now begin to
flow out of the exhaust port 48. This portion of the cycle is referred to
as blow-down. In FIG. 3D, at 180° in the operational cycle, the
inlet and exhaust ports 46 and 48 are open and pressurized air flows into
the cylinder 10 through the inlet port 46, while exhaust produced by
combustion flows out of the exhaust port 48. Scavenging now occurs as
residual combustion gasses are displaced with pressurized air. In FIG.
3E, at 193° the exhaust port 48 is closed by the piston 12, while
the inlet port 46 is still open due to the phase offset described above
and explained in more detail below. Charge air continues to be forced
into the cylinder 10 through the inlet port 46 until that port is closed,
after which the compression stroke begins. At 270° in the
operational cycle, shown in FIG. 3F, the pistons 12 and 14 are near
halfway through their compression stroke, and both the inlet and exhaust
ports 46 and 48 are closed. The pistons 12 and 14 then again move toward
their top dead center positions, and the cycle is continually repeated so
long as the engine operates.

[0045]FIG. 4 is a plot showing the phases of the pistons 12 and 14 during
the representative operational cycle just described. Piston phase may be
measured at either crankshaft referenced to the top dead center of each
piston. In FIG. 4, the axis M represents the distance of the crown of a
piston from its top dead center position, and the axis BB represents
phase. The position of the piston 12 is indicated by the line 50, while
that of the piston 14 is indicated by the line 52. At top dead center 60,
both of the pistons are in phase and the closed ends 12a and 14a are
equally distant from the longitudinal center of the cylinder 10. As the
operational cycle proceeds, the piston 12 increasingly leads in phase
until it reaches its bottom dead center point 61, just before 180°
in the operational cycle, indicated by 62. After the 180° point,
the piston 14 passes through its bottom dead center point 63 and begins
to catch up with the piston 12 until the two pistons are once again in
phase at 360° in the cycle.

[0046]The oscillating phase offset between the pistons 12 and 14
illustrated in FIG. 4 enables the desired sequencing of the inlet and
exhaust ports 46 and 48. In this regard, the line CC in FIG. 4 represents
the position of the crown of a piston where the port controlled by the
piston opens. Thus, when the closed end 12a of the piston 12 reaches the
point represented by 64 on CC, the exhaust port only is open. When the
closed end 14a of the piston 14 reaches the point represented by 65 on
CC, both ports are open and scavenging takes place. At 67 on CC, the
exhaust port closes and cylinder air charging occurs until the piston end
14a reaches the point represented by 68 on CC when both ports are closed
and compression begins. This desirable result arises from the fact that
the connecting rods for the respective pistons travel through different
paths during crankshaft rotation; while one rod is going over the top of
one crankshaft, the other is rotating under the bottom of the same
crankshaft.

[0047]It should be noted with respect to FIG. 4 that the respective
opening positions for the exhaust and inlet ports may not necessarily lie
on the same line and that their relative opening and closing phases may
differ from those shown.

[0048]As seen in FIGS. 2A, 2B, and 5A, the cylinder 10 includes a cylinder
tube 70 with opposing axial ends and annular exhaust and intake manifolds
72 and 74, each threaded, welded, or otherwise joined to a respective
axial end of the cylinder tube 70. The manifolds 72 and 74 may be
denominated the "cylinder exhaust manifold" and the "cylinder inlet
manifold", respectively. The manifolds 72 and 74 have respective internal
annular galleries 76 and 78 that constitute the exhaust and inlet ports,
respectively. Preferably each of the galleries 76 and 78 has the shape of
a scroll in order to induce swirling of gasses flowing therethrough,
while inhibiting turbulent mixing. Swirling the pressurized air
facilitates scavenging and enhances combustion efficiency. The cylinder
manifold 72 also includes an annular passage 77 surrounding the annular
gallery 76. The annular passage 77 may be connected to receive airflow,
or alternatively it may contain stagnant air, to cool the periphery of
the manifold 72. When the cylinder manifolds 72 and 74 are joined to the
cylinder tube 70, their outer portions are extensions of the common bore
of the manifolds and tube. The common bore may be precision machined to
closely match the diameter of the pistons 12 and 14, and the pistons and
cylinder may be fabricated from materials with compatible thermal
expansion characteristics. If ringless pistons (pistons without rings)
are used, there is no need for bridges spanning the ports, and a very
close tolerance may be obtained between the outer diameters of the
pistons and the inner diameter of the common bore. With ringless
operation, for example, the spacing between each piston and the bore may
be on the order of 0.002'' (2 mils or 50 microns), or less. The absence
of bridges also facilitates the formation of the intake manifold 74 into
a swirl inducing shape such as a scroll. If, on the other hand, the
pistons are provided with rings, it will be necessary to form the exhaust
and inlet ports as annular passages with annular sequences of openings to
the tube 70, thereby providing bridges to support the transit of the
rings past the ports. Tubes 82 and 84 formed on the cylinder manifolds 72
and 74 open into the internal annular galleries 76 and 78, providing
connection between the exhaust and inlet ports and respective exhaust and
inlet manifolds.

[0049]FIG. 5A is an enlarged side sectional view of the cylinder 10 with
opposed pistons 12 and 14 at their respective positions when the
operational cycle is near its 180° point. As suggested in FIGS.
3A-3F, and as shown in FIG. 5A, the pistons 12 and 14 are shown in these
figures without piston rings, although they may be provided with rings if
dictated by design and operation. Piston rings are optional elements in
this engine, for two reasons. First, piston rings accommodate radial
distortion of pistons and cylinders in order to assist in controlling the
cylinder/piston seal during engine operation. However, the cylinders
illustrated and described in this specification are not cast in an engine
block and are therefore not subject to non-uniform distortion from any
thermal stress or any mechanical stress generated by other engine
components, or asymmetrical cooling elements. As a result the cylinders
and pistons may be machined with very tight tolerances for very close
fitting, thereby confining combustion and limiting blow-by of combustion
products along the interstice between each piston and the cylinder.
Second, piston rings act to cool the piston during engine operation.
However, while the engine operates, each piston may be cooled by
application of liquid coolant because each piston is periodically
substantially entirely withdrawn from (or protrudes from) the cylinder as
it moves through its bottom dead center position so that liquid coolant
can be applied to its external surface. See FIGS. 2B, 3C and 5A in this
regard. As a piston moves out of and back into the cylinder, it is
showered (by dispensers to be described) with a liquid coolant on the
outer surface of its skirt. In addition, liquid coolant is applied (by a
dispenser 24 or 26) to its inner surface along its skirt up to and
including its crown.

[0050]For example, in FIG. 5A, each piston 12 and 14 is substantially
withdrawn from the cylinder 10 near its bottom dead center position.
Taking the piston 12 as representative, this means that, with the closed
end 12a of the piston 12 near the outer edge of the annular gallery 76,
the skirt 12s of the piston 12 is substantially entirely withdrawn from
the cylinder 10 while only the portion of the piston crown 12d between
the outside edge 760 of the gallery 76 and the outside edge 720 of the
exhaust manifold 72 remains in the exhaust manifold 72 fitted on the end
of the cylinder 10 as described below. It should be noted that each
piston 12 and 14 subsequently moves back into the cylinder 10 to the
extent that it is substantially enclosed by the cylinder 10 when it
reaches its top dead center position.

[0051]Thus, at its bottom dead center position, substantially the entire
skirt of each piston 12 and 14 protrudes from the cylinder 10 and is
exposed for cooling. The detailed description of how that occurs in this
illustrative example is not meant to limit the scope of this feature;
what is required is that enough of the outside surface of the skirt of
each of the pistons 12 and 14 be periodically outside of the cylinder 10
during engine operation to be sufficiently cooled by application of a
coolant to the outside surfaces of the skirts outside of the cylinder.
The percentage of the piston skirt that is exposed in a particular
application may vary based on a number of factors including, for example,
system coolant requirements, engine geometry, and designer preference.

[0052]As a piston moves in and out of a cylinder it is cooled by
application of a liquid coolant (by dispensers to be described) to the
outer surface of its skirt. In addition, liquid coolant is applied (by
dispenser 24 or 26) to its inner surface along its skirt up to and
including its crown. The same liquid coolant is preferably used to cool
both the interior and the exterior of the pistons. With reference to
FIGS. 5A and 6A, coolant dispensers, preferably made of steel tubing,
dispense a liquid coolant onto the pistons 12 and 14 and the cylinder 10
during engine operation. An elongate dispenser manifold 86 extends at
least generally axially along and against the cylinder tube and exhaust
and inlet manifolds 72 and 74. Four axially spaced semicircular
dispensers 86a, 86b, 86c, and 86d extend from the manifold tube halfway
around the cylinder 10. The dispenser 86a is positioned outboard of the
center of the exhaust manifold 72, near the outside edge 720; the two
dispensers 86b and 86c are located over the cylinder 10 between the
manifolds 72 and 74, preferably near the axial center of the cylinder 10
in order to apply proportionately more liquid coolant to the hottest
region of the cylinder than to other, cooler regions nearer the manifolds
72 and 74; and the dispenser 86d is located outboard of the center of the
inlet manifold 74, near the outside edge 740. A second dispenser manifold
tube 88 extends at least generally axially along and against the cylinder
tube and exhaust and inlet manifolds 72 and 74. Four axially spaced
semicircular dispensers 88a, 88b, 88c, and 88d extend from the manifold
tube 88 halfway around the cylinder 10. The dispenser 88a is positioned
outboard of the center of the exhaust manifold 72, near the outside edge
72o; the two dispensers 88b and 88c are located over the cylinder between
the manifolds 72 and 74, preferably near the axial center of the cylinder
10 in order to apply proportionately more liquid coolant to the hottest
region of the cylinder than to other, cooler regions nearer the manifolds
72 and 74; and the dispenser 88d is located outboard of the center of the
inlet manifold 74, near the outside edge 74o. Opposing dispensers are
linked together as at 89 for structural integrity. Alternatively, the
dispensers may be entirely circular and connected to a single manifold
tube. Further, fewer or more dispensers may be provided and may be
differently positioned than as shown. Still further, the dispensing
branches could be replaced by a number of circumferentially spaced
nozzles or sprayers supplied with liquid coolant from a common source.

[0053]The dispensers have substantial apertures formed thereinto from
which a liquid coolant under pressure is applied to exposed outside
surfaces of the skirts of the pistons 12 and 14 and the outside surface
of the cylinder tube 70. Preferably, dispensers are positioned near the
respective outside edges of the manifolds in order to ensure that liquid
coolant is applied to substantially the entire outside surface of the
skirt along the axial length of each piston. Depending on factors such as
system coolant requirements, engine geometry and designer preference, the
dispensers, nozzles, or other suitable coolant application elements may
be repositioned in order to dispense or apply liquid coolant to smaller
percentages of the outer radial peripheral surface areas of the skirts.
For example, liquid coolant may be applied to the outside or external
surface of the skirt along at least 25%, 50%, or 75% of the axial length
of each piston.

[0054]In FIGS. 5A and 6A, the liquid coolant dispensers that apply liquid
coolant to the outside surfaces of the pistons and cylinder are shown as
being separate elements; however, one or more dispensers may also be
integral with the cylinder manifolds 72 and 74 in addition to, or instead
of, the separate elements shown in the figures.

[0055]In an alternate embodiment shown in FIG. 5B, instead of cooling the
cylinder tube 70 by way of dispensers, the cylinder tube may be disposed
in a jacket 87 to provide a cooling passage 90 around the cylinder
through which the coolant may be circulated. In this case, dispensers
would still be used to cool the pistons.

[0056]The open structure of the saddles 16 and 18 and the absence of
wristpins in the pistons permit improved direct application of liquid
coolant to the internal surfaces of the pistons. In this regard, as shown
in FIGS. 2A, 2B, and 5A, the pistons 12 and 14 are continuously cooled
during engine operation by application of liquid coolant through
dispensers 24 and 26 to their interior surfaces including their domes
along their skirts to their open axial ends.

[0057]In FIG. 5A, the flow of liquid coolant onto the pistons and the
cylinder is indicated by reference numeral 91.

[0058]Continuing with the description of FIG. 5A, annular,
high-temperature polymeric rings 92 located in annular grooves near the
ends of the manifolds 72 and 74 lightly contact the pistons 12 and 14 and
wipe excess lubricant from the pistons as they travel into the cylinder
10. Finally, one or more fuel injectors are provided for the cylinder.
For example, the fuel injector 94 is coupled to the at least one
injection site 95.

[0059]A two-stroke, opposed-piston engine mechanism is next described in
which the working elements (cylinders, pistons, linkages, crankshafts,
etc.) are received upon a structural unit in the form of a frame of
passive structural elements fitted together to support the working
elements. The frame is intended to bear the stresses and forces of engine
operation, such as compressive forces between the crankshafts. In
contrast with many prior art two-cycle, opposed-piston engines, the
cylinders are not cast in a block nor are they formed with other passive
structural elements. Consequently, the cylinders are not passive
structural elements of the engine. Each cylinder is supported in the
engine frame principally by the pair of pistons disposed in it. Thus,
with the exception of combustion chamber forces, the cylinders are
decoupled from the mechanical stresses induced by functional elements,
and from the mechanical and thermal stresses of an engine block. Hence,
the cylinders are essentially only pressure vessels. This engine
construction eliminates non-uniform radial distortion of the pistons and
cylinders, permits the cylinder-piston interface to be very
close-fitting, and enables a close matching of the thermal
characteristics of the materials from which the cylinders and pistons are
made. Advantageously, with improved piston cooling, this characteristic
affords the option of an engine design that dispenses with the need for
piston rings.

[0060]FIGS. 6A and 6B are side perspective views showing increasingly
complete assembly of a single-cylinder engine mechanism 100 for an
opposed-piston engine with side-mounted crankshafts based on the
cylinder/piston arrangement of the previous figures. The engine mechanism
100 can be scaled to engines of any size and engines having from one to
multiple cylinders. In FIG. 6A, the mechanism 100 includes a single
cylinder 10 having the construction illustrated in FIG. 5A, with opposed
pistons 12 and 14 disposed in it. The saddles 16 and 18 of the opposed
pistons are visible in the figure. The connecting rods 20a and 20c couple
the saddle 16 to the crankshaft 30, and the connecting rod pair 20b
couples the saddle 16 to the crankshaft 32. The connecting rod pair 22a
couples the saddle 18 to the crankshaft 30, and the connecting rods 22b
and 22c couple the saddle 18 to the crankshaft 32. The dispenser manifold
tube 88 and the dispenser 24 are connected to coolant manifold 96. The
manifold tube 86 and the dispenser 26 are connected to another coolant
manifold 98. Two radially-opposed alignment pins (one of which is
indicated by reference numeral 99) are formed on the cylinder 10 for
cylinder stabilization during engine operation. Two beams 110 and 112 are
shown in FIG. 6A for reference. The beam 110 has an opening 113 through
which the manifold tube 84 can be connected to an air inlet manifold (not
shown) and an opening 115 for a tube connecting the fuel injector 94 to a
fuel manifold (not shown). The beam 112 has an opening 117 through which
the manifold tube 82 can be connected to an exhaust manifold (not shown)
and an opening 119 through which a tube can connect another fuel injector
(not seen) to a fuel manifold (not shown).

[0061]In FIG. 6B, a frame for the engine mechanism 100 includes two
support bulkheads 120 disposed on respective sides of the cylinder 10,
together with the beams 110 and 112. The bulkheads 120 receive and
support the crankshafts 30 and 32. Each bulkhead 120 includes an I-beam
section 122 and a transverse section 124. The I-beam sections provide the
principal stress relief for the crankshafts during engine operation. The
beams 110 and 112 are attached to the ends of the transverse sections
124. The crankshafts are supported for rotation in the I-beam sections
122 by bearings 128. Each bulkhead includes a central opening with a
short elastomeric cylinder 132 that receives alignment pins 99 of
adjacent cylinders. Threaded holes 134 are provided in each support
bulkhead for attachment of additional components, for example, a gearbox.

[0062]Assembly of a single-cylinder opposed piston engine module from the
engine mechanism 100 of FIGS. 6A and 6B is shown in FIGS. 7A-7D. In the
single-cylinder engine module, light aluminum end plates 160 and 162 are
attached to respective bulkheads 120 and to each of the beams 110 and
112. The end plate 160 has openings 163 and 164 to receive the liquid
coolant manifolds 96 and 98 to feed lines (not shown). FIGS. 7A, 7B and
7D show a gearbox 170 mounted on a bulkhead (not seen in these figures)
through the outside surface of the end plate 160. The gearbox 170 houses
an output gear train through which the opposing rotational motions of the
crankshafts are coupled to an output drive shaft. The ends of the
crankshafts 30 and 32 extend into the gearbox 170. A gear wheel 172 with
a toothed outer rim is fixed to the end of the crankshaft 30 and a gear
wheel 173 with a toothed outer rim is fixed to the end of the crankshaft
32. An output gear wheel 175 has an annulus 176 with a toothed inside
circumference 177 and a toothed outside circumference 178. As seen in
these figures, the outer rim of the gear wheel 172 engages the inside
circumference 177 of the gear wheel 175 at one location and the outer rim
of the gear wheel 173 engages the outside circumference 178 of the gear
wheel 175 at another location diametrically opposite the one location.
The gear ratio between the inner gear 172 and the inside circumference
177 may be 33/65 with MOD 4 teeth on the inner gear and the inside
circumference, while the gear ratio between the outer gear 173 and the
outside circumference 178 may be 33/65 with MOD 5 teeth on the outer gear
and the outside circumference. This arrangement of gears permits the
opposing rotations of the crankshafts 30 and 32 to be translated into the
continuous rotation of the output gear wheel 175 with an odd number of
gears (three, in this case), with a non-integral gear ratio, and without
any intermediary belts, chains, or other torque transfer elements. The
result is a simple, short output gear train.

[0063]Assembly of the single-cylinder opposed piston engine module is
completed as shown in FIG. 7c by attachment of light aluminum casing
panels 180 to the frame made up of the assembled bulkheads and beams. A
cover 182 is fastened to the gearbox 170. The cover 182 includes an
output bearing 185 that receives the axle 186 of the output gear wheel
175 thus enabling the frame to support the output gear 175 for rotation.
The resulting assembled single-cylinder opposed-piston engine module is
indicated by reference numeral 190 in FIG. 7c. The axle 186 constitutes
the output drive of the engine module 190. It may be coupled to an
intermediate transmission or directly to the driven component by one or
more gears, belts, chains, cams or other suitable torque transfer element
or system (not shown).

[0064]FIGS. 8A-8C illustrate assembly of a multi-cylinder, opposed-piston
engine module with three engine mechanisms 100 disposed in a row. Note
that the front and rear bulkheads are removed from FIG. 8A for clarity.
The mechanisms 100 have the structure already illustrated in FIGS. 6A and
6B, and discussed in respect of the preceding figures. Four bulkheads 120
are provided in the frame of this engine module, each supporting the
crankshafts in respective bearings. The frame also includes elongated
beams 110 and 112 fixed to the transverse sections of the bulkheads 120.
The end plates 160 and 162 close the ends of the engine module. The
three-gear drive train is supported for rotation in the gearbox 170. The
liquid coolant manifolds 96 and 98 are elongated to span the three engine
mechanisms 100. Assembly of the multiple-cylinder opposed piston engine
module is completed by attachment of light aluminum casing panels 180 to
the frame. A cover 182 is fastened to the gearbox 170. The cover 182
includes an output bearing 185 that receives the axle 186 of the output
gear wheel 175 thus enabling the frame to support the output gear wheel
175 for rotation. The resulting assembled multiple-cylinder
opposed-piston engine module is indicated by reference numeral 290 in
FIG. 8c. The axle 186 constitutes the output drive of the engine module
290.

[0065]The best mode for carrying out an opposed-piston internal combustion
engine according to the principles thus far described and illustrated
includes providing four identical connecting rods for each piston. This
mode of practice is best seen in FIG. 6A. In the view of FIG. 6A, on the
exhaust port side of the cylinder 10, the two connecting rods 20a and 20c
are spaced apart and each is connected at one end to the saddle 16 and at
the opposite end to the crankshaft 30. The connecting rod pair 20b
comprises two abutting rods, each identical in shape and structure to the
rods 20a and 20c. The connecting rod pair 20b is connected at one end to
the saddle 16, and at the other end to the crankshaft 32. On the input
port side of the cylinder 10, the two connecting rods 22b and 22c are
spaced apart and each is connected at one end to the saddle 18 and at the
opposite end to the crankshaft 32 on either side of the connecting rod
pair 20b. The connecting rod pair 22a comprises two abutting rods, each
identical in shape and structure to the rods 22b and 22c. The connecting
rod pair 22a is connected at one end to the saddle 18, and at the other
end to the crankshaft 30, between the connecting rods 20a and 20c. Thus,
on each of the crankshafts, the connecting rod pairs of the pistons on
one end of the cylinders are interleaved with the two connecting rods of
the pistons on the other end of the cylinders, as shown in FIG. 6A. This
provides an optimum balance of forces on the pistons and also reduces the
count of part types for the engine. The identical rods also assist in
maintaining uniform thermal expansion of the rods during engine
operation.

[0066]The best mode also includes connecting rods of forged steel or
titanium, cylinders and pistons of aluminum-silicon alloy with
chrome-plated cylinder bores, liquid coolant-conducting elements of steel
tubing, and crankshafts of forged, machined steel. Engine frame parts may
be made of lightweight alloys such as aluminum.

[0067]A supply system 300 for supplying a liquid coolant to be dispensed
on and in pistons and on cylinders in an opposed-piston engine of one or
more cylinders is illustrated in FIG. 9A. The liquid coolant may be any
liquid capable of being applied to the pistons and cooling them
sufficiently for the desired application. Lubricating oil and diesel fuel
are two possibilities. In this figure, a source of liquid coolant 310 is
connected to a low-pressure, high-volume pump 312. The pump 312 may
comprise, for example, a centrifugal pump providing liquid coolant in the
range of 3 to 10 gal/min for a 100 HP engine. which pumps liquid coolant
through a distribution line 313 to the manifolds 96 and 98. These
manifolds supply a high volume of liquid coolant at low pressure to the
dispensers 24 and 26 and to the dispensing manifolds 86 and 88 of one or
more modules 100. The liquid coolant is collected by a sump 315 in the
opposed-piston engine. A pump 317 connected to the sump pumps the
collected liquid coolant through a filter 318 and a radiator 319 back to
the source 310. As seen in FIG. 9A, a line 320 may be provided in
parallel with the radiator 319. In this case, a valve 321 would control
liquid coolant flow through the radiator 319 and a valve 322 would
control liquid coolant flow through the line 320. For normal operation,
only the valve 321 would be open, permitting liquid coolant to flow
through the radiator 319, thereby dissipating the heat of the pistons and
cylinders via the radiator 319. For short term boosted operation, the
valves 321 and 322 would both be open, thereby dissipating the heat of
the pistons and the cylinders via the radiator 319 and absorbing some of
the heat in the reservoir of liquid coolant in the source 310. Finally,
during emergency operation in the event of radiator failure the valve 321
would be closed and the valve 322 would be open, thereby temporarily
diverting the heat of the pistons and cylinders into the reservoir of
liquid coolant.

[0068]If an opposed-piston engine is operated as a compression-ignition
engine, fuel injection is the method of delivering diesel fuel to the
cylinders for combustion. In this case, diesel fuel also preferably
serves as the liquid coolant and as the lubricant for the pistons. It is
therefore possible to combine the fueling and coolant sources,
eliminating the need for multiple sources. Referring to FIG. 9B, a system
400 for supplying diesel fuel to be dispensed on and in pistons and on
cylinders and supplied to fuel injectors in an opposed-piston engine of
one or more cylinders is illustrated. In this figure, a source of diesel
fuel 410 is connected to a low-pressure, high-volume pump 412 (a
centrifugal pump, for example) which pumps liquid coolant through a
distribution line 413 to the manifolds 96 and 98. These manifolds supply
a high volume of liquid coolant at low pressure to the dispensers 24 and
26 and to the dispensing manifolds 86 and 88 of one or more engine
mechanisms 100. The diesel fuel is collected by a sump 415 in the
opposed-piston engine. A pump 417 connected to the sump pumps the
collected diesel fuel through a filter 418 and a radiator 419 back to the
source 410. A return line 420 parallel to the radiator 419 is provided.
Valves 421 and 422 control the use of the radiator 419 and return line
420 as explained above in connection with the valves 321 and 322 in FIG.
9A. A pre-pump 423 connected to the source 410 pumps diesel fuel through
a filter 424, and to a high-pressure pump 426, which boosts the pressure
of fuel delivered to the injectors. For example, the pump 426 may supply
diesel fuel at 30,000 psi. The fuel from the pump 426 is supplied through
an input fuel line 427 connected to a common rail 429 and the input ports
of one or more fuel injectors 94. The return ports of the one or more
fuel injectors are returned through line 430 to the source 410. An
electronic control unit (ECU) 431 controls the operations of the one or
more fuel injectors 94.

[0069]Another advantage of an engine built according to this specification
is that all of the bearings used to support the crankshafts and
connecting rods may be roller bearings. These bearings may be lubricated
by being sprayed with diesel fuel, whose lubricity and viscosity at the
operating temperatures of an opposed-piston engine are completely
adequate for their lubrication.

[0070]Thus, by way of the pump 412, the system 400 may deliver diesel fuel
as a lubricant for all bearings of the engine, save those in the gearbox
170. In this regard, as diesel fuel supplied from the dispensers, the
diesel fuel is churned into a mist within the engine that spreads
throughout the engine and works its way between the moving parts of the
engine and into the rolling bearings contained within the engine. A
single source can then be used to supply such coolant, and lubricant to
the engine.

[0071]An alternate supply system 350 for supplying a liquid coolant to be
dispensed on and in pistons and on cylinders in an opposed-piston engine
of one or more cylinders is illustrated in FIG. 9C. This system may be
used for dispensing liquid coolant alone as the system 300 in FIG. 9A, or
it may be combined with other elements in a system for dispensing diesel
fuel to cool, lubricate, and fuel an engine as illustrated in FIG. 9B.
The liquid coolant may be any liquid capable of being applied to the
pistons and cooling them sufficiently for the desired application.
Lubricating oil and diesel fuel are two possibilities. In this figure, an
engine enclosure 352 enclosing one or more engine mechanisms 100 contains
a sump region 357 where liquid coolant emitted by the above-described
dispensers is collected. The liquid coolant collected in the sump region
357 has a nominal operating fluid level 358. A source valve 359 is
mounted in the engine enclosure. A level sensor 360 in contact with the
liquid coolant collected in the sump region 357 controls a linkage 361
that selects the state of the source valve 359. The source valve 359 has
an output connected to a low-pressure high-volume pump 362. The pump 362
may comprise, for example, a centrifugal pump. The source valve 359 has
two inputs, a first connected to a feed line 363 from the sump region
358, and a second connected to a feed line 364 from a supply tank 366
containing the liquid coolant. The pump 362 pumps liquid coolant through
a feed line 367 to a filter 368 and therethrough to a radiator 369. From
the radiator 369, the liquid coolant flows through a feed line 370 to the
manifolds 96 and 98. These manifolds supply the high volume of liquid
coolant at low pressure to the dispensers 24 and 26 and to the dispensing
manifolds 86 and 88 of one or more modules 100. For example, the liquid
coolant may be provided in the range of 3 to 10 gal/min for a 100 HP
engine. As seen in FIG. 9C, a thermal valve 372 is connected in parallel
with the radiator 369 between the output of the filter 368 and the feed
line 370. The state of the thermal valve 372 is controlled by the
temperature of the liquid coolant or by an emergency circuit 373. The
emergency circuit 373 is also connected to the source valve 359. A level
valve 375 has an input connected in common with the output of the filter
368, the input of the radiator 369, and the input of the thermal valve
372. The output of the level valve 375 is connected through a feed line
377 to the supply tank 366. The control linkage 361 is also connected to
control the state of the level valve 375.

[0072]With further reference to FIG. 9C, in normal operation, the level
sensor 360 detects the level of liquid coolant in the sump region 357 and
selects as a source for the pump 362 either the sump region 357 or the
supply tank 366. When the operating level has been reached, the level
sensor sets the control linkage 361 to place the source valve in the
state where it draws liquid coolant only from the sump region 357. The
heated liquid coolant is pumped by the pump 362 through the filter 368 to
the radiator 369 and the thermal valve 372. When a design operating
temperature of the liquid coolant is achieved, the thermal valve will
close partially or fully to modulate the flow of liquid coolant through
the radiator 369, thereby regulating the engine temperature. The flow of
liquid coolant continues through the feed line 370 to the dispensers
where the liquid coolant is applied to remove heat from the engine
components. If the level of liquid coolant in the sump region becomes too
high, the level sensor 360 causes the control linkage 361 to partially
open the level valve 375 to return a portion of the liquid coolant to the
supply tank 366 after filtration at 368. In an emergency situation where
it is necessary to temporarily bypass the radiator 369, the emergency
circuit 373 fully opens the thermal valve 372, thereby shunting the
radiator 369, and forces the source valve 359 to initially draw liquid
coolant from the supply tank 366. The excess liquid coolant that
accumulates in the sump region 357 will be removed by the level valve in
response to the level sensor 360. For temporary maximum performance, the
thermal valve 372 is closed, thereby utilizing the full capacity of the
radiator 369, while the state of the source valve 359 is set to draw
fluid only from the supply tank 366.

[0073]A system 500 for providing charge air to and discharging exhaust
gasses from an opposed-piston engine is illustrated in FIG. 10. The
system may scale to serve one or more cylinders 10. In the system 500, an
air inlet manifold line 534 and an exhaust outlet manifold line 532 are
respectively connected to the inlet port tubes 84 and the exhaust port
tubes 82 of one or more modules. These manifold lines are preferably
mounted outside the engine enclosure. The engine schematically
illustrated in FIG. 10 is a turbo-supercharged or supercharged engine.
Thus, the manifold lines are connected to a turbo-supercharger 536.
Specifically, the exhaust gases moving through the exhaust manifold line
532 drive a turbine 540 en route to an output line 538 to mechanically
drive a compressor 542. The compressor 542 draws air in on an air inlet
line 537 and pressurizes the intake air before directing air to the inlet
manifold line 534 by way of an intercooler 539.

[0074]Other engine elements not included in the illustrations will be
provided according to specific circumstances of each application of this
opposed-piston engine. In this regard, the gearbox 170 may be sealed and
self-lubricated by oil or may be lubricated separately from the rest of
the engine. Alternately, it could be left open and lubricated by the
coolant/lubricant used to cool and lubricate the pistons, provided that a
suitable lubricant is employed.

[0075]In prior engines, as the BMEP increases, friction at the piston
ring/cylinder interface increases and the interface temperature rises.
The increasing interface temperature ultimately results in heat flowing
back into the piston from the interface rather than from the piston to
the interface. As a consequence, the rings no longer cool the piston.
Assuming maximum flow of coolant to the inside surfaces of the piston
skirt and crown, the only remaining piston surfaces to cool are the
exterior surfaces of the skirt and crown. The exterior surface of the
crown is a component of the combustion chamber and is only marginally
cooled by combustion gas expansion and scavenging airflow; this surface
is otherwise inaccessible to external cooling. In prior art engines, the
exterior surface of the piston skirt is also inaccessible to piston
cooling because the piston is encased in the cylinder. However, with
periodic exposure of the external surface of the piston skirt by
substantially withdrawing the piston from the cylinder bore, that surface
is available for cooling. As a result, on the order of twice the amount
of heat transfer is achievable when compared with cooling only the inside
surfaces of the piston skirt and crown. Enhanced engine performance is
thereby realized, with the result that opposed-piston engines constructed
according to this specification are capable of achieving improved BMEP,
specific output, and PWR when compared with prior art opposed-piston
engines. For example an opposed-piston engine constructed according to
this specification will tolerate BMEP of at least 200 psi, at least 250
psi, or at least 300 psi due to improved cooling. Such an opposed-piston
engine is capable of providing specific power densities (SPD) of at least
11.0 HP/in2, at least 12.0 HP/in2, or at least 13.0
HP/in2. These improvements enable this opposed-piston engine to
achieve a PWR of at least 0.5 HP/lb., at least 0.667 HP/lb, or at least
1.0 HP/lb.

[0076]The uses and applications of this opposed-piston engine are
manifold. It can be scaled for any application using two-cycle engines,
including two-cycle diesel engines. The engine can be installed in or
mounted on a variety of powered vehicles, tools, devices, or other
apparatus requiring the delivery of rotary power. See FIGS. 11A-11D for
examples in this regard. In FIG. 11A, this two-cycle opposed-piston
engine 1100 is installed in a surface vehicle, which can include wheeled
or tracked vehicles, such as automobiles, motorcycles, scooters, trucks,
tanks, armored military vehicles, snow-mobiles, and all equivalent and
similar instances. In FIG. 11B, this engine is installed in a water-going
vehicle such as a boat, hovercraft, submarine, personal water craft, and
all equivalent and similar vehicles. In FIG. 11C, this engine is
installed in a fixed or rotary-wing aircraft. In FIG. 11D, this engine is
installed in a powered implement such as a lawnmower, edger, trimmer,
leaf blower, snow blower, chain saw, and all equivalent and similar
devices. In FIG. 11E, this engine is installed in an electrical power
generating device. In FIG. 11F, the engine is installed in a pumping
device.

[0077]Although the invention has been described with reference to specific
illustrations and examples, it should be understood that various
modifications can be made without departing from the spirit of the
principles of our engine. Accordingly, the invention is limited only by
the following claims.